Science

No one truly knows how the images were formed. Attempts to show
how they might have been formed have been a complete failure. The
best explanations remain highly speculative.

The one thing science has succeeded in doing is proving that the
images
were not painted, are not some form of medieval proto-photography or
any other known artistic method. This does not mean, as some in the
media often report, that proponents of authenticity believe the images
were miraculously formed. It only means nobody knows.